The present invention relates to power conversion apparatus and methods, and more particularly, to power conversion apparatus and methods in which a polyphase AC output is generated from a DC link.
Uninterruptible power supplies (UPSs) are commonly used to provide conditioned and/or auxiliary power to electronic equipment that provides critical functions, such as computer systems, telecommunications systems and medical equipment. Typically, UPSs can provide AC power from a backup source, such as a battery, generator or fuel cell, in the event that a utility power supply fails or becomes degraded.
Some UPS systems use an architecture in which an AC voltage is generated from a DC voltage on a DC link. As shown in FIG. 1, a typical conventional double-conversion UPS 100 includes a rectifier 110 that receives AC power from an AC power source 10, such as a utility grid. The rectifier 110 generates a DC voltage on a DC link 115. The UPS 100 further includes an inverter 120 that generates an AC output that is applied to a load 20 from the DC voltage on the DC link 115. The DC link 115 typically includes first and second busses, respective voltages of which are typically balanced on positive and negative sides of a neutral of the AC output. Backup or supplemental power may be provided via the DC link by an auxiliary DC power source 130, e.g., a battery.
FIG. 2 illustrates a conventional “line interactive” UPS architecture. A line-interactive UPS 200 includes an inverter/charger circuit 220 that is configured to be coupled to an AC source 10 and a load 20. The inverter/charger circuit 220 is operative to act as an inverter when the AC source 10 has failed or become degraded, generating an AC voltage to power the load 20 from an auxiliary power DC power source 230, e.g., a battery, coupled to the inverter/charger circuit 220 by a DC link 215. When the AC source 10 is in a normal state, the inverter/charger circuit 220 may act as a rectifier, supplying charging current to the auxiliary source 230 over the DC link 215. Similar to the double-conversion configuration of FIG. 1, the DC link 215 typically includes first and second busses, respective voltages of which are typically balanced on positive and negative sides of a neutral of the AC output/input.